Police have long used helicopters. But in Alameda County, a controversy is brewing over a much smaller aircraft. ABC7 News was there as the sheriff unveiled two new drones that are already facing opposition.

The sheriff's office uses all kinds of expensive robots. Some have wheels, some have treads, nearly all have cameras. But there's one robot that's drawing all the attention. It's one with propellers.

When asked why he felt the need to hold a news conference on Wednesday, Sheriff Greg Ahern said, "Because these systems are very controversial."

The controversy erupted in Feb. of 2013. Standing beneath a giant model of a predator drone, civil rights groups begged Alameda County supervisors to block the sheriff's purchase of the small quadcopters. He wants them to help search and rescue workers and swat teams with a barricaded suspect.

"It's not easy to send people in front of harm's way on a daily basis when you know you have proper tools and equipment that make them safer and you don't deploy them," said Ahern.

Nearly two years later, the sheriff's announced he's done waiting. He's bought two of the copters with encrypted controllers and infrared cameras.

"The cost was approximately $97,000," Ahern said.

The sheriff says the extra cost is because this is no ordinary drone. Beyond having the special certifications for law enforcement use, it's also specially designed for gathering evidence that could later appear in court.

"This drone could be flying all over the county, including over my house," said ACLU Technology Policy Director Nicole Ozer.

The American Civil Liberties Union worries they'll gather evidence against protesters and activists.

"Today the sheriff may say he's gonna use it for one purpose," Ozer said. "Tomorrow it could be used to surveil communities of color throughout Alameda County. we just don't know."

"I have no intention as long as I'm sheriff to utilize these devices for surveillance purposes," Ahern said. "Absolutely none."

Still, the sheriff says he'd oppose outlawing it.

"We have a device up and we locate a marijuana field, they want us to turn a blind eye to the fact that we located a marijuana field with that device," he said.

He says he talked at length with the ACLU, but apparently not recently.

"The sheriff and his office have not reached out to us in more than a year," Ozer said.

They said they were shocked that he went ahead with the purchase and they'll be asking county supervisors for laws to limit the use of the eye in the sky.